This invention relates to combined heat pump and hot water systems that provide heating of an indoor air space, or cooling of the indoor air space, and in which the amount of refrigerant, i.e., the charge of the system, is automatically adjusted based on thermal demand.
Integrated heat pump systems of this type have a compressor and indoor and outdoor heat exchanger coils, and in many cases, an integral water heat exchanger. Compressed refrigerant flows through the water heat exchanger and gives up superheat to water in the heat exchanger. Then the compressed refrigerant vapor flows via a reversing valve to either the indoor coil (for heating mode) or to the outdoor coil (for cooling mode). There the refrigerant is condensed and liquid refrigerant proceeds through a condensed refrigerant line to the other of the heat exchanger coils, where it passes through an expansion device into the coil, and the condensed refrigerant evaporates and picks up heat. Hot water is provided in either a cooling mode or heating mode.
Where neither space heating nor cooling is called for, the system can still provide water heating and the water heat exchanger rejects the bulk of the refrigerant heat into the water. In that case the heat exchanger fan associated with the condenser coil is kept off, but that of the evaporator coil is actuated on. For example, when the reversing valve is set for a heating mode, but space heating is not called for, the indoor fan is not run. On the other hand, when the reversing valve is set for cooling, but cooling is not called for, the outdoor fan is not run. Superheat and condensing heat are rejected into the water.
Air conditioning and heating (i.e. air-to-air) heat pumps must operate over a wide range of conditions, and have expansion device characteristics and refrigerant charge levels selected to optimize the balance between performance and reliability over this range. If there is a high refrigerant charge provided, the system will operate more effectively under high demand conditions, but may flood the system in times of low demand, and, vice versa, if less charge is provided performance suffers during times of high demand. To provide sufficient refrigerant charge over the entire range of conditions without overcharging the system during times of lower demand, some means to adjust the refrigerant charge level of the heat pump system should be incorporated. However, no suitable charge adjustment mechanism has been previously provided.
Bos et al. U.S. Pat. No. 4,893,476 employs a liquid storage receiver to store unneeded refrigerant in a heat pump system. However, this arrangement relies on rather expensive thermal expansion valves to meter the circulating flow.
Derosier U.S. Pat. No. 4,299,098 includes a refrigerant charge control in a space heating, cooling, and water heating heat pump system to keep the refrigerant from becoming trapped within an inactive heat exchange means. During times of heavy load excess refrigerant is directed into the inactive heat exchange means by actuating a number of four-way valves.
Glamm U.S. Pat. No. 4,528,822 employs a charge reservoir to store refrigerant charge, and controls charge by removing charge to the reservoir in some modes but returns the charge from the reservoir in other modes of operation. Valves to the reservoir open or close depending only on the mode of operation rather than on the refrigerant pressure or temperature at the compressor.